The present invention relates to a line of manufacturing units for carrying out a sequence of machining operations on a set of workpieces, which are fed in, in succession, at one loading end of the line and proceed along the line up to an unloading end of the line, in which said line comprises means for transfer of the workpieces from the end for loading onto the first unit in the line, from each unit of the line to the next, and from the last unit in the line to the unloading end.
In lines of the kind referred to above, which are made up of a succession of manufacturing units or work centres, it is already general knowledge that it is possible to have available devices for transfer of the workpieces from one unit to another on the line. In more traditional systems, transfer devices are provided, which simultaneously cause all the workpieces that are on the line to advance by one step along the line. This traditional solution is, however, not particularly efficient. In general, in fact, the various units along the line carry out cycles of operations of different duration. With a rigid transfer system of the type described above, it is, however, necessary for all the units to have completed their respective cycles of operations in order to be able to start carrying out the step of transfer of each piece from one unit to another. In addition, the rigid transfer system according to conventional techniques enables only limited variations in the angular position of the piece during its transfer. The piece may, in fact, normally translate only in a position where it is resting on a surface or, more in general, in conditions of stability of its centre of gravity, and can, at the most, only turn about a vertical axis, unless auxiliary devices are added, designed for turning the workpiece upside down before or after the travel of transfer.
In the past, there have been proposed transfer devices of a flexible type, in which between each unit of the line and the next there is set a transfer device, which operates independently from the other transfer devices in order to reduce dead time as much as possible during the production cycle. The present applicant has, for example, presented various robotic solutions (see, for example, the U.S. Pat. No. 5,522,275) designed for transferring workpieces between the workstations of a production line of any type. Of course, transfer devices in the form of robots present the drawback of being relatively costly and cumbersome and of penalizing accessibility and cleanliness of their working areas, and hence are not always suitable for application to a line of machining centres. On the other hand, there is increasingly felt the need to step up productivity, particularly in the automobile field, also following upon the trend that has appeared in the last few years of concentrating a number of production sites in a single plant.
In the specific field of lines for carrying out machining (for instance, a production line for cylinder heads for motor-vehicle engines), the need for high productivity is always accompanied by the need for maximum reduction in production costs. A solution of a line of machining centres provided with devices for transfer of workpieces from one unit to another in the line is described in the Japanese patent application JP-A-11 114 783. This known device envisages transfer devices, each of which is made up of a pair of arms, which are mounted in an articulated way, underneath, about a horizontal axis and oscillate with their top ends through a vertical arc between two end positions, one end being adjacent to one unit of the line set upstream of the transfer device and the other end being adjacent to a second unit of the line set downstream of the transfer device. This known solution presents the drawback of being relatively complicated and of not being efficient. In particular, in so far as the pieces are transferred along an arched path and consequently must be raised from the starting position to reach the apex of the arc, with a consequent useless expenditure of energy. A further drawback of the aforesaid known solution lies in the fact that the transfer devices are mounted on the floor, on which the line is set out, and consequently entail an encumbrance which reduces accessibility to the various units in the line. A further drawback of the above known solution is that the workpiece can be transferred only in a single position. In addition, there is a penalization in terms of accessibility and of the possibility of cleaning the working area, as well as the requirement that the workpiece must be fixed on a dedicated pallet, specifically shaped for the workpiece that is to be transferred.
The purpose of the present invention is to provide a line of manufacturing units for carrying out machining operations with removal of stock, which will be equipped with means for transferring workpieces from one unit to another in the line and which will be able to overcome all the drawbacks of the prior art that have been discussed above.
With a view to achieving the above purpose, the subject of the invention is a line of manufacturing units of the type referred to at the beginning of this description, characterized in that the aforesaid transfer means include:
a fixture made up of a plurality of horizontal supporting and guide beams, which are set in a superelevated position with respect to the floor on which the line is set, said beams extending in the longitudinal direction of the line, each one of which in a position corresponding to a space comprised between one manufacturing unit and another adjacent one;
a transfer device mounted on each of the aforesaid supporting and guide beams, said device comprising:
a first mobile slide, which can move along the respective supporting and guide beam in the longitudinal direction of the line;
a vertical upright mounted upon said first mobile slide, which, in one example of embodiment, constitutes a second mobile slide, which can move vertically;
pick-up means, which are mounted on the bottom end of said second slide or upright and which can be oriented about a vertical axis;
motor means for controlling the first slide, second slide (if provided) and said pick-up means; and
control means designed for controlling the motor means of the various transfer devices of the line independently of one another, but according to a sequence preferably co-ordinated together in such a way that, when any single manufacturing unit has terminated its cycle of operations on a piece, the transfer device downstream of said unit is already waiting nearby to pick up the workpiece that has undergone machining, and the transfer device upstream of the unit is already waiting nearby, with a new workpiece loaded upon it, in order to be able to unload it onto the unit so that it will undergo the corresponding operating cycle.
Preferably, the various manufacturing units have respective orientable tables for supporting the workpiece, and the aforesaid superelevated horizontal supporting and guide beams of the various transfer devices substantially all extend at the same height and are arranged substantially so that one is on the prolongation of the other.
Thanks to the above-mentioned characteristics, the transfer means with which the line according to the invention is equipped are made up of modular translating devices, which enable the operations of transfer of the workpieces from one unit of the line to another to be carried out in an extremely efficient manner, with an extremely simple and low-cost structure as compared to a system which uses robots. The various transfer devices have a modular structure, which can be easily reconfigured according to the specific requirements of the line. Since the transfer devices are mobile on superelevated beams, they do not entail any additional encumbrance which might constitute an obstacle to accessibility to the units of the line or render cleaning operations more problematical. The transfer of the pieces from one unit to another can be carried out without causing the workpiece being transferred to undergo substantial variations in height, so as to simplify equipping for carrying out transfer operations (a vertical upright may be sufficient instead of the second vertically mobile slide) and to avoid high power absorption by the motor means associated to the transfer devices.
According to a further preferred characteristic, there can be associated to one or more transfer devices magazines for the accumulation of the workpieces, where the transfer device can provisionally deposit a workpiece, whilst waiting for the manufacturing unit downstream thereof to become free, or else can carry out on the piece inter-operational checks in order to guarantee the quality of the piece undergoing machining.
By accordingly prearranging the pick-up device, it is moreover possible to perform an action of turning the piece over, i.e., setting it in an upside-down position, in order to discharge any chips or swarf (xe2x80x9cchip dumpxe2x80x9d) and cutting liquid that may have accumulated inside the piece during the previous machining phase, without having to add sophisticated and cumbersome devices, as instead is necessary with other known solutions.
Owing to its characteristics, the transfer device which forms part of the line according to the invention is suited for handling pieces of any shape and ones set in any position.